Clutch brakes are devices that slow and stop the rotation of a transmission input shaft to facilitate shifting of gears, particularly in large vehicles, such as over-the-road trucks.
Transmissions on class 8 over-the-road trucks are not fully synchronized, which requires the input shaft from the transmission to be completely stopped before shifting into first or reverse gears. One method is to stop the truck, shut off the engine, shift into the desired gear and restart the engine. Because of the inconvenience of stopping the truck to perform these steps, clutch brakes have been added to stop the input shaft, thereby permitting shifting of gears while the truck is in motion.
Most such clutches are pull-type clutches, wherein the throw-out bearing is pulled towards the transmission to shift gears. To shift into first or reverse gears, the throw-out bearing is pulled back to make contact with the clutch brake and the front of the transmission, which causes a squeezing effect that stops the transmission input shaft from turning. The gears are then shifted and the clutch throw-out bearing is released completing the shift action.
Pull-type clutches are adjustable by turning an internal ring that compensates for wear of the clutch disc and flywheel surfaces. When an internal adjustment is made, the clutch is returned to original specifications, as the clutch requires specific clearance to prevent premature failure of the clutch. When the flywheel is new and a new clutch assembly is installed, there is approximately ½ inch clearance between the clutch brake and the throw-out bearing. When installing new clutch assemblies, flywheels should be resurfaced to eliminated the wear effects of the previous clutch on the flywheel, or alternately, the flywheel should be replaced. The bearing cap retainer, located on the front of the transmission where the clutch brake contact also wears and should be replaced with a new bearing cap. However, the bearing cap retainer should preferably not be resurfaced. Every time the flywheel is resurfaced by grinding, the clutch assembly moves closer to the engine and farther from the clutch brake and transmission. Most flywheels are resurfaced numerous times, so the ½ inch dimensional clearance increases. Wear of the bearing cap on the transmission also causes an increase in this gap.
During installation, clutch brakes are commonly installed over the input shaft between the transmission and the clutch. The input shaft has a keyway, wherein internal tangs extending from the clutch brake engage the keyway to permit the clutch brake to stop the rotation of the input shaft.
Specifically, the clutch brake rides on the transmission input shaft and is disposed between the clutch assembly and the transmission. The input shaft typically has two keyways disposed therein, wherein the keyways cooperatively engage with tangs on the clutch brake. The clutch brake further comprises an approximately ⅜ inch thick plate assembly having frictional surfaces on both ends thereof.
An example of such internal tangs are screw fasteners. However, as is commonly experienced, screw fasteners can loosen with time and become unfastened, thereby diminishing the functionality of same, and potentially causing damage to critical drive train components.
In addition to internal tangs, external tabs are typically found on clutch brakes, wherein such external tabs provide connection points for attachment of the clutch brake to a frame. Unfortunately, however, such attachment point tabs are fixed and immovable once attached to a frame mount, thereby preventing any adjustment of the clutch brake.
Other devices provide two separate plates secured via threads, wherein the plates are restrained from rotation by a bolt extending into one of the plates, and wherein the bolt secures a jockstrap that sits in a detent in the other plate, thereby preventing rotation of same. However, the aforementioned jockstrap and fastener therefor can loosen due to general vehicular vibration, thus causing unexpected adjustment of the clutch brake, and/or causing damage to critical drive train components.
Still other devices provide an adjustable clutch made from two half-circular sections, wherein the two sections are fastened together via bolts extending through the sections. In such devices, the bolts serve as tangs to engage the keyway of an input shaft and, as such, can loosen with general vehicular vibration and time; thereby, resulting in disengagement of the bolts from the input shaft, and/or damage to critical drive train components. The device further lacks an adjustment mechanism, thereby requiring replacement of same when such adjustments are needed.
Some devices provide arms bolted to a portion of the outer of two plate sections, wherein the arms extend and latch beneath bars disposed on the inner of two plate sections. However, such devices are not clutch brakes, but rather clutches themselves, and further are not adjustable. Accordingly, such devices unable to slow rotation of a clutch and must be replaced when adjustment is necessary.
Additional devices include the use of frictional pads or similar materials on the surface of the clutch brake; however, such frictional pads do not facilitate adjustment of a clutch brake pack and, therefore, are unsuitable for varying dimensional requirements or field replaceability.
Therefore, it is readily apparent that there is a need for a clutch brake that can be adjusted while installed on a vehicle without the need for special tools, and which does not loosen during use; thus, avoiding the above-described disadvantages.